Update

At 2am Dean's wind speeds went back up to 150mph (from 145mph) and the NHC notes that Dean "COULD BECOME A CATEGORY FIVE HURRICANE TODAY".

Using dead reckoning of the track over the last 6-12 hours, I think it's safe to say that the center of the storm will pass far enough south of the Cayman Islands to spare them the worst of the storm. At this point Grand Cayman should already be getting tropical storm force winds, though.

Currently the NHC is forecasting Dean to be a Category 5 hurricane upon landfall on the Yucatan Peninsula early Tuesday morning.